Radio transmitters generate the modulated signals required for wireless communications using modulation techniques such as QPSK, 8-PSK, 16-QAM, 64-QAM, and OFDM. These techniques vary the amplitude, phase, and/or frequency of the transmitter's RF carrier.
An I/Q modulator provides a convenient and straightforward method to realize the modulation. It uses quadrature signals to drive double-balanced mixers that combine to form the transmit signal. Unfortunately, the mixers generate noise and operate inefficiently. This causes problems in low-noise, low-power applications. It would therefore be advantageous to reduce the mixer's current consumption while lowering its output noise level.